Once you set it to RAID 0 in BIOS, everything else will recognize your RAID 0 set up as a single 73GB drive. Windows shouldn't know the difference with the exception of the RAID 0 driver you'll be using. (Of course your system config will say RAID 0)

The real benefit from 10k drives is that they have fast seek times, like SCSI drives of the like. This means for example, if you're in game and there a tiny piece of information that the computer didn't put on your RAM, which it needs, when it goes to the HDD, it won't take as long to pull, and place it on the RAM. The benefit of RAID 0 is different. When you initially call up data, it's seek time, but after that when you're transfering, say, a large chunk of data, then because you have 2 drives working to pull all that data, it will be.... "twice as fast" (not really but similar).

If you put it into perspective of a warehouse, having RAID 0 is like having 2 guys run around the warehouse picking an order, and having 10k is like having a guy that can run around really fast picking an order. Ideally you want 2 guys (RAID 0) that can run around really fast (10K) picking the order.

I say you should get the 2 Raptors and then later, when you need more space, get a dirt cheap large capacity drive for the ATA100 connector, for storage. Use the twin Raptors for the OS, programs and frequently accessed stuff, or you could get the deluxe version mobo which has 2 RAID 0 controllers, and get 2 dirt cheap drives later and RAID 0 them as well.

I think the 875 and 865 chipsets are supposed to support the P5. PCI Express doesn't look like something you need. Apart from those things, all other advances will be minor, like 1066 FSB. If you always wait for what's faster, then, you'll never end up buying anything. I've been playing that game for 3 years.